At least in the US, when you are attending a degree program, a lot of times you can pick between several different types of classes to fulfill a specific requirement. For example, maybe you have the option to either take plant biology or invertebrate biology and it will satisfy the same requirement. So you choose plant biology because it interests you more.

And then there are often multiple class times available for some of the larger classes. So you can slightly tailor your education to different interests and your own schedule.

Except when I went to grad school…all of my classes were preselected for me in the way that you stated they were for you.